At the beginning of the story, Sam, who is the narrator, gives several reasons why he and Bill choose Summit for their kidnapping scheme. As Sam says in the text:
There was a town down there, as flat as a flannel-cake, and called Summit, of course. It contained inhabitants of as undeleterious and self-satisfied a class of peasantry as ever clustered around a Maypole.
The word "undeleterious" means harmless, and Sam refers to the inhabitants of Summit as "peasantry." Here, O. Henry's language reveals Sam and Bill's attitude toward the citizens of Summit. Sam and Bill think that it will be easy to pull off the kidnapping because the people of Summit are simple, rural folk who won't put up a fight, so to speak. Another quotation from the beginning of the story demonstrates the same attitude:
Philoprogenitiveness, says we, is strong in semi-rural communities; therefore and for other reasons, a kidnapping project ought to do better there than in the radius of newspapers that send reporters out in plain clothes to stir up talk about such things. We knew that Summit couldn't get after us with anything stronger than constables and maybe some lackadaisical bloodhounds and a diatribe or two in the Weekly Farmers' Budget. So, it looked good.
"Philoprogenitiveness" means to have a love for children or to produce many offspring. Sam characterizes a rural town like Summit as a place where people love children and have close-knit families; therefore, citizens of Summit would be outraged by a kidnapping and pay any amount of money necessary to get their children back. Furthermore, Sam figures that, because Summit is such a small town, he and Bill won't face any real trouble or challenges to their scheme. As Sam puts it, a few constables and a rant in the newspaper won't put a damper on their plan to get $2000. Of course, the situational irony of the story is that Sam and Bill mischaracterize Summit; their incorrect assumptions about the town are partly what lead to their downfall. Sam and Bill end up kidnapping Red Chief, a boy who is so mischievous and uncontrollable that Red Chief's own father seems to want the boy off of his hands (as do the inhabitants of Summit).